* CEO to step down in September

* New CEO to be named in 12 months

*

(Adds background on MacLennan leadership throughout, background on M&C's campaigns in paragraph 11 and 12)

July 24 (Reuters) - British advertising group M&C Saatchi Plc said its Chief Executive Moray MacLennan, the last founding member still at the advertising group, will step down at the end of September.

MacLennan, 61, who has been with the company since its inception in 1995, became CEO in 2020 and through various roles had overseen the group's growth from a single London advertising agency to a global network operating in 30 countries.

"M&C Saatchi is well set for the future and now is the right time to make way for fresh energy and ideas," MacLennan said in a statement on Monday.

MacLennan, a British national, had led the company through takeover talks with its biggest investor Vin Murria and consultancy Next Fifteen Communications in 2022, which were eventually rejected by the advertising group.

He took over as CEO after the company was faced with accounting probes related to its annual results in 2019, which led to its co-founder Maurice Saatchi quitting the board.

A new CEO is expected to be named within the next 12 months, and newly appointed Non-Executive Chair Zillah Byng-Thorne will act as executive chair from Sept. 1, the company said.

MacLennan's exit comes amid weak revenue at the group and at a time when the ad industry is grappling with competition from new technology tools such as artificial intelligence, evidenced by a statement from S4 Capital.

The original Saatchi & Saatchi business, led by the Saatchi brothers before they set up M&C Saatchi, made a name for itself with its "Labour isn't working" campaign poster for Margaret Thatcher showing a queue of people snaking out from an unemployment office and disappearing into the distance.

M&C Saatchi was responsible for the "remain" campaign during Brexit referendum.

MacLennan will step down on Sept. 30. (Reporting by Radhika Anilkumar in Bengaluru; Editing by Subhranshu Sahu and David Holmes)